docs: async def _defaultExpectHandler(request):  # pragma: no cover
      """Default handler for Expect header.
  
      Just send "100 Continue" to client.
      raise HTTPExpectationFailed if value of header is not "100-continue"
      """
      expect = request.headers.get(hdrs.EXPECT)
      if request.version == HttpVersion11:
          if expect.lower() == "100-continue":
              request.transport.write(b"HTTP/1.1 100 Continue\r\n\r\n")
          else:
              raise HTTPExpectationFailed(text="Unknown Expect: %s" % expect)